The Gherkin is an astonishing building and could be one of Lord Foster's finest architectural achievements. It totally dominates the City skyline and, as a City of London guide taking groups on walking tours of the Square Mile, I am frequently asked questions the structure. The Gherkin is a symbol of modern London but for me this is a place of nearly 2,000 years of remarkable history. Come with me and I'll tell you about it sometime.